There has conventionally been known an automatic charging system which includes an automatic charging apparatus which is mounted on a vehicle and adapted to operate as follows. The apparatus obtains position information representing position of the vehicle by use of, for example, GPS and on the basis of the position information judges (determines) whether the vehicle has entered a charged area. When the vehicle is judged to have entered the charged area, the apparatus calculates a charge amount, and subtracts the calculated charge amount from the balance of a prepaid card, an IC card, or a like card, to thereby collect a toll or a like fee.
In such system, an important factor is that the automatic charging apparatus function properly. In view of this, Japanese Patent Application Laid-Open (kokai) No. 11-306402 discloses a system including an automatic charging apparatus configured to cause a light emitting element or a like element to blink in a special pattern or configured to change the frequency or the like of a radio wave to be transmitted in a special pattern so as to communicate to the outside the state of charging; and a monitor apparatus which detects the blinking of the light emitting element, for example, and judges on the basis of the detection result whether the automatic charging apparatus functions properly.
However, in the conventional system, the detection of the pattern of blinking of the light emitting element or the detection of the frequency, for example, of the radio wave is performed while the vehicle travels. Therefore, there is a possibility that a normal automatic charging apparatus is misidentified as an anomalous automatic charging apparatus of another vehicle.